1. Technical Field
The present invention relates to switching mechanisms applicable to video cameras and, more particularly, to a structurally simplified, novel switching mechanism for a video camera, wherein the switching mechanism serves to smoothly and quietly switch filters of the video camera without using any complex control unit.
2. Description of Related Art
For a general video camera equipped with a CCD or CMOS element to maintain a satisfactory image-capturing state in daytime as well as at night, it is necessary to switch filters for diurnal and nocturnal use of the video camera respectively such that high image fidelity is achieved in the day, and clear pictures can be taken during nighttime. Therefore, filter-switching mechanisms, i.e., structures with a filter-switching function, are commonly provided in video cameras.
Filter-switching mechanisms can be controlled by several methods, and from the perspective of control, the existing filter-switching mechanisms may be sorted into the following two types.
The first type is the “closed-circuit control mechanisms”, which are the most basic and popular automatic switching mechanisms. In such a mechanism, employed in either a mechanical device or an optical device, feedback sensors are provided at a starting point and a terminal point of the switching operation. The feedback sensors detect the positions of objects being switched and output electronic signals to a control chip so that the control chip actuates or stops a driving device (usually a motor) accordingly, thereby realizing the desired switching function. Although this approach is capable of monitoring the conditions of the objects being switched, as well as providing reliable control over the objects, it is nevertheless disadvantaged by high costs and bulky design.
The other type is known as the “open-circuit control mechanisms”. In such a mechanism, an input unit provides a positive control function in a one-way manner so that a motor drives an object without detecting conditions thereof. This type of mechanisms are advantageously simple and economical because no complex controllers and feedback mechanisms are required. However, since there are no position sensing devices (e.g., switches and sensors) for determining the conditions of the driven object, once the object is blocked from moving but the driving device (e.g., a motor) is not timely stopped, components along the driving link, such as the motor or a transmission mechanism (most probably the motor), are likely to be damaged. Therefore, to protect the components, it is necessary to incorporate into the control mechanism a mechanism for making and breaking the connection between the driven object and the driving device. One of the most popular solutions is control by frictional constraint. While this friction-based solution is mechanically simple and economical, it has such inherent and unconquerable defects as blindness toward the conditions of the driven object and significant operational noise.
Thus, there is a need for a novel switching mechanism that is applicable to video cameras and capable of eliminating all the above problems.